A current electro-luminescent display is of a self-emitting type and does not require a back light unlike a liquid crystal display (LCD), and thus weight reduction and slimness thereof are feasible. Further, the electro-luminescent display has a low driving voltage, a high luminous efficiency and a wide viewing angle, thus receiving attention as a next generation display.
Light emitting display devices can be generally classified into two types—transparent and conventional non-transparent displays. Transparent displays are simultaneously top and bottom emitting devices, have a reasonably high transmittance of visible light and can be used in the applications that require transparency, such as head-up displays, smart windows or augmented reality, but they cannot be used for non-transparent displays. Conventional non-transparent displays can emit light only in one direction, being either bottom light emitting devices or top light emitting devices. Although non-transparent displays have significantly higher brightness and efficiency compared to transparent displays, they cannot achieve transparent display for a reason that a conventional non-transparent display has one electrode with a reflective surface which reflects the generated light toward a second, transparent or semi-transparent, electrode. In contrast, a transparent display has two transparent or semi-transparent electrodes, and the light is emitted through both sides of the display.
The existing light emitting display devices are either transparent or non-transparent display devices, unable to work for both transparent display and non-transparent display, and thus are poor in operation convenience.